The aim of the tissue core is to provide a morphology service to all projects and to support the breeding and maintenance of the mice. All projects in this proposal will require extensive use of morphological techniques to meet their goals, and it is cost effective to allocate these duties to a core. The second function of this Core is to establish and maintain a facility that allows the breeding of mice (wild type, chimera, and transgenics) and we propose to use one skilled technician to carry out all these tasks. Again it is core cost effective to have these duties controlled by the core.